Method for preparing ferrocarbon intermediate product for use in steel manufacture and furnace for realization thereof

ABSTRACT

The hereinproposed method and furnace provide for preliminary building up of melt in a melting pot (10) of a rectangular shape in the horizontal section, delivery of an oxygen-containing gas (3) into the melt below its surface level through tuyeres (13) with nozzles (14) installed in the longer walls of the melting pot (10) creating two melt zones: an upper zone (9) loaded with solid carbon fuel (2) in an amount sufficient for providing a volumetric concentration of said fuel within 0.5 to 50% of the melt volume in said zone (9), wherein said concentration is maintained by subsequent concurrent loading of iron-bearing material (1) and solid carbon fuel (2), and a lower zone (8) consisting of a layer of slag (4) and a layer of ferrocarbon intermediate product (5) said layers being discharged separately through channels (17 and 18) made in the counterproposed short walls of the melting pot (10). The ratio of the horizontal section area of the melting pot (10) at the installation level therein of tuyeres (13) to the total area of the outlet holes of the nozzles (14) is 300-10000, while the distance (h) from the lower boundary of the product discharge channel (18) to the upper boundary of the slag discharge channel (17) is 0.3 to 0.75 the distance (H) from the lower boundary of the product discharge channel (18) to the installation level of the tuyeres (13).

FIELD OF THE ART

The invention relates to ferrous metallurgy and, more particularly, to amethod for preparing a ferrocarbon intermediate product for use in steelmanufacture, and to a furnace for realization thereof.

Most successfully the present invention can be utilized in processingpartly reduced or raw iron-ore materials for the preparation of anintermediate product used in steel manufacture.

The present invention can also be used to advantage for utilization ofiron-bearing rejects of metallurgical industry such as dried sludges,dusts liberated in gas purification, scale, as well as small-lumpferrous metal scrap, particularly chips.

PRIOR ART

Nowadays the basic method for preparing a ferrocarbon intermediateproduct for use steel making is blast-furnace melting which yields castiron from iron ore materials including those reduced in advance andmakes it possible to rework partly iron-bearing rejects includingsludge, scrap and chips. However, the blast-furnance melting calls forpreliminary preparation of iron-ore raw materials by modulizing i.e. bysintering or making pellets; besides, the reducing fuel used inblast-furnace melting is a high-quality metallurgical coke which can bemade from a limited number of expensive coking coals whose worlddeposits are dwindling down at a fast rate. Thus, the blast-furnacemelting, apart from the blast-furnace practice proper, calls for havinga by-product coke industry and a production of sinter or pellets.

Besides, effective blast-furnace melting requires raw materials with ahigh iron content, i.e. as a rule, previously enriched raw materials.Lean and hard-to-enrich ores are practically uneconomical.

Another prerequisite for efficient blast-furnace melting is asufficiently large production volume. In small-scale production theblast-furnace melting proves inefficient.

A further disadvantage of blast-furnace melting lies in that thechemical composition of its product, i.e. cast iron can be changedwithin very narrow limits. This complicates the steel making technology.

In addition, blast-furnace melting allows but a small amount of rejectsto be utilized in the charge. The use of rejects affects adversely theperformance of the furnaces and the process indices. For example, theuse of metallurgical sludges introduced into the charge for producingsinter, cuts down the output of the blast furnaces and steps up theconsumption of coke because of the formation of zinc skull in thefurnaces.

The above-stated disadvantages of the blast furnace process, of whichthe use of coke in the main one, gave an impetus to the creation of anew branch of metallurgy, so-called coke-free metallurgy. Up to thepresent time there appeared a number of new technological processes andproduction layouts which can be classified into the following maintrends.

The first trend includes processes for the preparation of ferrocarbonintermediate product, these processes being dependent on the use ofelectric power and being carried out in electric furnaces. When thecharge in these processes is contituted by iron ores or theirconcentrates, these processes are, as a rule, multistage. Electricmelting is preceeded by heating and preliminary solid-phase reduction ofthe raw material. In most effective processes Elred and Inred belongingto this trend and developed of late in Sweden, the use of electric poweris partly supplemented by the energy of coal burnt in oxygen. However,even in these processes the consumption of electric power remains high.Besides, they still utilize a certain amount of coke. The processesdependent on the use of electric energy can prove effective only oncondition that the production of said electric power utilizes theprocess flue gases. However, even in this case high losses sustained intransmission of energy and multiple transformations will render saidprocesses less effective than those in which the energy of fuel isutilized directly.

Another trend widely pursued of late includes methods of preparation ofa ferrocarbon intermediate product through the use of noncoking coal andgaseous oxygen for melting partly reduced raw material in converter-typeunits. To this trend belong the processes COIN, KS, the process of theJapanese firm Sumitomo, etc. They are based on injection of pulverizedcoal in a stream of oxygen into the metal bath. A portion of coal burnsup in oxygen, forming CO and releasing heat required for melting. Theother portion of coal is used for carburization of metal. When thecharged raw material melts, the iron oxides move into slag where theyare reduced by carbon dissolved in metal.

The reducing gas evolved in these processes is utilized for preliminaryreduction of iron-ore raw materials. Thus, the mechanism of preparingthe intermediate product from iron-ore raw material for steelmanufacture is divided into two stages. Another disadvantage of thisgroup of processes is the use of pulverized coal whose preparationinvolves heavy difficulties. Besides, pneumatic transportation ofpulverized coal in the stream of oxygen is highly complicated. A seriousproblem is the strength of the refractory lining of the furnace. The useof cooled elements in the furnace instead of refractories when the metalbath is boiling due to the interaction of carbon dissolved in it withthe oxides of slag iron is virtually impossible.

A specific trend is represented by the processes, wherein the reducinggas liberated from the melt (mostly CO) is utilized directly in amelting-reduction furnace rather than in another unit (e.g. forpreliminary reduction of the raw material for burning to heat the rawmaterial, to produce steel electric power. This trend also embraces suchprocesses as Dored, Eketorp-Vallak, etc. These have been activelypursued and developed in the 50s and 60s. Their merits include simpletechnology and equipment, single-stage nature attained by reburning theprocess gases directly in the furnace. However, the heat of reburning isutilized not sufficiently well. Therefore, these processes have notenjoyed wide recognition. More than that, owing to a successfuldevelopment of solid-phase reduction of iron-ore raw materials, recentyears have witnessed mostly the processes involving no reburning, sincethe gas produced in these processes can be used as a reducing agent insolid-phase reduction of iron-ore raw materials.

However, if the processes without reburning are to be sufficientlyeffective, it is expedient that their charge should consist ofpre-reduced iron-ore raw materials produced by solid-phase reduction.

Most closely approaching the present invention with respect to thetechnical essence and the effect sought for is a method for preparationof ferrocarbon intermediate product for use in steel manufacture,comprising simultaneous loading of an iron-bearing material and solidcarbon fuel and delivery of an oxygen-containing gas, their interaction,in which the oxygen of the oxygen-containing gas oxidizes part of thefuel, releasing the heat expended for melting the iron-bearing materialand reducing the metal oxides it contains with the carbon of theremaining fuel accompanied by the formation of liquid products ofmelting, viz., slag and ferrocarbon intermediate product and processgases and, lastly, discharging the liquid products of melting andprocess gases. This method is realized with the aid of a furnacecomprising a melting pot with a hearth, a stack resting on a meltingreservoir and provided with at least one device for charging theiron-bearing material and solid carbon fuel into the melting pot locatedin the top part of the stack, a tuyere with nozzles for the delivery ofoxygen-containing gas into the melting pot which has a slag-dischargeduct made in the wall of the melting pot, at its hearth, and a duct fordischarging the ferrocarbon intermediate product made in the wall of themelting pot below the installation level of the tuyeres with nozzles,and a means for discharging the process gases from the stack, located inthe upper part thereof. (Inventor's Certificate of the USSR No. 1169995,C1C12B 13/00 published in the Bulletin "Discoveries, Inventions,Industrial Designs and Trademarks" No. 28, 1985).

The known method is realized as follows. At the beginning of melting themelting pot of the furnace is charged with coke acting as a packing,then oxygen-containing gas is fed through tuyeres and an iron-bearingmaterial is loaded on top of coke through an appropriate device. Afterburning up the coke (coke packing), melting the iron-bearing materialand reducing the oxides of its metals the resultant melt consists of ametal and slag. Then an oxygen-containing gas is delivered above thesurface of the melt and the place of coke is taken by a solid carbonfuel (coal) which starts to be loaded from above together with theiron-bearing material (sponge iron). A part of fuel (coal) is oxidizedin the oxygen-containing gas to CO, while the liberated gases ascend,creating a fluidized bed of coal particles above the melt. The releasedheat creates a sufficiently high temperature is said bed. The heat ofthe high-temperature zone is transmitted by radiation to the meltreceiving the iron-bearing material that continues falling from above.In the course of its fall through the furnace stack said material ispartly heated, then, floating on the slag surface or inside it melts,forming a liquid metal, i.e. a ferrocarbon intermediate product forsteel manufacture, which goes down and accumulates on the hearth underthe layer of slag. The liquid products of melting, i.e. metal and slag,are discharged either continuously or intermittently. This method alsoprovides for the use of crushed iron-ore raw materials withoutpre-reduction, and of the fine ore of non-iron materials. The upper partof the fluidized bed of coal above the delivery level of theoxygen-containing gas may be supplied with liquid or gaseoushydrocarbons.

The known method and the furnace for realization thereof areinsufficiently economical, which is attributable to a number of factors.

Since the main heat-mass transfer processes take place in the fluidizedbed of coal, this calls for high rates of oxygen feed and high dischargevelocities of process gases formed. This results in high losses of coaland the handled iron-bearing material which are carried out in the formof dust. The size of particles of the iron-bearing material and fuelshall be kept within narrow limits selected in response to the velocityof discharged gases. Otherwise, the small fractions will be carried overfrom the furnace while the larger ones will get into the layer of slagunmelted and insufficiently heated.

Inasmuch as the slag is in quescent state, its heat-absorbing surface islimited by the bath surface area and the heat exchange in the layer ofslag is difficult because of its low heat conduction. Therefore, theparticles of the material falling into slag are slowly heated and meltedand the slag surface becomes covered with a layer of sufficiently largelumps of fuel that cannot be held in the fluidized bed. Featuring but alow heat conduction, these lumps hinder heat transfer from thehigh-temperature zone to slag, because said heat transfer occurspredominantly by way of radiation.

If the iron-bearing material is constituted by iron-ore raw material(ore, concentrate or sponge iron) characterized by an insufficientlyhigh degree of reduction, iron oxides of these materials will enter theslag. Reduction of iron from slag can be achieved due to the effect ofthe carbon of the fuel lumps floating on the slag surface or due to thecontact of the slag with the reducing atmosphere of the furnace.However, both processes have low speeds because the phase contactsurface is limited by the surface area of the slag bath and the speed ofmass transfer in slag is low due to poor stirring.

All the above factors result in a low efficiency of the processes and,as a consequence, in overexpenditure of fuel and insufficient yield ofmetal, i.e. iron which is lost with the slag, particularly when thelatter is discharged continuously. Besides, the known method and thefurnace for its realization impose substantial limitations both on thechemical and granulometric composition of the iron-bearing material andfuel.

DISCLOSURE OF THE INVENTION

The cardinal object of the present invention resides in providing amethod for preparing ferrocarbon intermediate product for use in steelmanufacture comprising a number of technological processes which wouldcreate a large interface area between the phases: oxygen-containinggas--solid carbon fuel--melt and intensify the heat-mass transferprocesses of interaction between the iron-bearing material, solid carbonfuel and oxygen-containing gas, and a furnace for the realization ofsaid method, wherein the stack and melting pot would be so designed andthe tuyeres feeding the oxygen-containing gas into said pot would be soarranged relative to said pot as to ensure a high efficiency of themethod at a low consumption of solid fuel and high extraction of metalfrom the iron-bearing material

This object is achieved by providing a method for preparation offerrocarbon intermediate product for use in steel manufacture,comprising simultaneous loading of the iron-bearing material and solidcarbon fuel, delivery of oxygen-containing gas, interaction of theiron-bearing material, solid carbon fuel and oxygen-containing gas inwhich the oxygen of the oxygen-containing gas oxidizes part of the fueland releases the heat used for melting the iron-bearing material andreducing the metal oxides contained therein by the carbon of theremaining part of fuel, forming liquid products of melt, i.e. slag andferrocarbon intermediate product and process gases and discharging theliquid products of melt and process gases in which, according to theinvention, simultaneous loading of the iron-bearing material and solidcarbon fuel is preceded by building up slag melt and theoxygen-containing gas is delivered into slag melt below its surface sothat the stream of gas bubbles the melt and divides it into two zones,viz. the lower quiescent zone and the upper zone bubbled by thedelivered gas and loaded with solid carbon fuel in a quantity sufficientfor creating in this zone a volumetric concentration of fuel within 0.5to 50% of the melt volume in this zone, the iron-bearing material andsolid carbon fuel being simultaneously loaded into the upper zone with aview to maintaining the produced concentration of fuel, which, duringinteraction of the iron-bearing material with the solid carbon fuel andoxygen-containing gas, ensures the formation of liquid slag entering thelower zone and forming a slag layer therein and of liquid metal in theform of drops passing through the slag layer and creating under saidlayer a layer of ferrocarbon intermediate product, the liquid productsof melting, i.e. slag and ferrocarbon intermediate product beingdischarged separately from the corresponding layers of the lower zone.

The preliminary building up of the slag melt and making a volumetricconcentration of solid carbon fuel in its upper bubbled zone rangingfrom 0.5 to 50% allows the melting process to be started quickly withoutthe use of the initial coke packing. Creation of the bubbled upper zoneof the melt by delivering oxygen-containing gas, then delivering thesolid carbon fuel and iron-bearing material into said zone provide for alarge interface area between the phases: solid fuel--gas--melt and foran accelerated heat-mass transfer processes. As a result of oxidation ofsome solid carbon fuel in the melt, the produced gas has a high partialpressure of carbon monooxide (CO) which takes part in the reduction ofmetal, iron for one, from slag. The concentration in the bubbled zone ofsolid carbon fuel is maintained during melting (depending on the kind offuel, properties of slag and other parameters) within the limits from0.5 to 50% so as to provide conditions in the slag for efficientreactions of reduction. At fuel concentrations below 0.5% the reductionreactions cannot take place due to a high partial pressure of oxygen inthe gaseous phase and an insufficient surface of interaction between theiron-bearing material, solid carbon fuel and oxygen-containing gas. Atfuel concentrations higher than 50% the melt in the bubbled zone losesits fluidity, as a result of which the heat-and mass transfer in thebubbled zone is impaired. The formation in the lower zone of the pot ofa quiescent zone consisting of a layer of slag and a layer of metalpermits, on the one hand, improving the quality of separation of metalfrom slag and, on the other hand raising the stability of the refractorylining in this zone. All this taken together permits raising theefficiency of the process, thus reducing the specific consumption ofsolid carbon fuel and increasing the extraction of iron from theiron-bearing material.

In the course of melting it is expedient that the oxygen-containing gasshould be delivered into the slag melt at the rate of 150 to 1500 Nm³ /hper m² of the horizontal section area of the melt at the level where theoxygen-containing gas is delivered into said melt.

At a consumption below 150 Nm³ /h per m² of the horizontal section areaof the melt at the level where the oxygen-containing gas is deliveredinto said melt, the conditions of melt stirring are impaired and theheat-mass transfer processes are retarded, thus bringing about a lowerefficiency and reduced extraction of iron. The consumption rates over1500 Nm³ /h per m² of the horizontal section area of the melt at thelevel where the oxygen-containing gas is delivered into said melt maybring about throwout of the melt and reduction of iron extraction due toa large volume of the oxidizing tuyere zones.

In the course of melting it is expedient that the flow rate of theoxygen-containing gas fed into the slag melt be increased in response tothe increase in the reactivity of solid carbon fuel. All otherconditions being equal, this may conduce to a higher output. Conversely,when passing over from the fuel with a high reactivity to the fuel witha low reactivity, it is good practice to reduce the amount of thedelivered oxygen-containing gas. Otherwise the partial pressure ofoxygen in the gaseous phase will rise, thereby increasing the losses ofiron with slag.

The solution of this problem is promoted also by the fact that theoxygen-containing gas may be delivered into the slag melt continuously,with periodic interruptions in the concurrent loading of theiron-bearing material and solid carbon fuel.

This permits a reduction in the sulphur content in the resultingferrocarbon intermediate product due to periodic refining from sulphurof the slag melt bath used in the process.

It is also expedient that the slag melt should be built up by pouring inliquid slag produced in the manufacture of ferrous metals, e.g. whenmaking cast iron in blast furnaces, steel in converters, open-hearthfurnaces and electric furnaces.

The liquid synthetic slag melted in advance in an electric or some otherfurnace can also be poured in.

To speed up the beginning of continuous melting, (in continuousproduction of metal) and to reduce wear of the refractory lining, it isgood practice to pour liquid metal into the furnace before pouring inliquid slag.

If pouring in of liquid slag into the furnace is impossible for somereason or other, the slag melt can be built up by loading in and meltingat least one of the solid oxide materials selected from the groupconsisting of slags produced in ferrous metallurgy, mineral rawmaterials and metal oxides.

In addition to the solid carbon fuel it is possible to deliver gaseous,liquid or solid pulverized carbon-containing fuel into the upper zone ofthe melt, below its surface level.

This delivery will improve the working conditions of tuyeres, speed upthe interaction of carbon with the oxygen of the oxygen-containing gasthus contributing to reducing the volume of the zones with an oxidizingatmosphere inside the melt at the point of injection of theoxygen-containing gas.

To step up the stability of the process, it is expedient that the slagbe withdrawn from the lower zone at the level of the middle or upperparts of the slag layer.

This will make it possible to produce a very slightly stirred layer ofslag above the surface of the metal bath in the furnace. Short-termvariations of the iron oxide content in the slag of the upper bubbledzone resulting from variations in the composition of the charge willbring about changes in the composition of slag in the upper and middleflowing parts of its layer. The composition of the lower part of theslag layer in the lower zone will change very slowly. This staves offits sharp overoxidation and fluidizing of the metal bath due to theevolution of the reaction of decarburization which may disturb theprocess and cause throwing out of the melt. This improves the stabilityand reliability of the process.

To increase the efficiency of fuel utilization, it is good practice inthe course of melting that the oxygen-containing gas should beadditionally delivered above the melt surface in an amount of(0.01-5.0)×10³ Nm³ per ton of solid carbon fuel. In this case the oxygenof the oxygen-containing gas reburns CO and H₂ released from the melt asa result of incomplete fuel combustion and reduction of iron oxides withcarbon, to CO₂ and H₂ O. This is accompanied by liberation of aconsiderable amount of heat part of which is conveyed to the melt andutilized for carrying out the process. The delivery of theoxygen-containing gas at the rate of 5.0×10³ Nm³ per ton of solid carbonfuel is quite sufficient for complete reburning of the gases emittedfrom the bath. The delivery of the oxygen-containing gas in an amountexceeding 5.0×10³ Nm³ per ton of fuel increases the content of freeoxygen (O₂) in the discharged gases, causes overexpenditure of oxygencontaining gas and impairs the thermal performance of the furnace. Thedelivery of the oxygen-containing gas in an amount lower than 0.01×10³Nm³ per ton of solid carbon fuel is impracticable, since there occurs noreburning and oxygen is spent only for gasifying the fine solid carbonfuel thrown out of the melt.

When melting is conducted with additional delivery of theoxygen-containing gas above the melt surface (with reburning) withconcurrent loading of iron-bearing material and solid carbon fuel, thelatter should better be taken in the amount of 0.2 to 5.0 t/h per m² ofthe horizontal section area of the melt at the level of feeding theoxygen-containing gas into said melt.

These limits are based on the hydrodynamics of the bath and thermalconditions of the process, on intensities of delivery ofoxygen-containing gas into the melt and above its surface. An amount ofsolid carbon fuel less than 0.2 t/h per m² of the horizontal sectionarea of the melt at the level of delivery therein of theoxygen-containing gas prevents achieving a low partial pressure ofoxygen in the melt, which reduces the ectraction of metal from theiron-bearing material into the intermediate product and increases thelosses of metal with slag. The amount of solid carbon fuel exceeding 5.0t/h per m² of the horizontal section area of the melt at the level ofdelivery thereto of the oxygen-containing gas brings about supersaturation of the melt with solid carbon fuel, reduces the flowabilityof the melt and slows down the processes of heat-and-mass exchange;this, in turn, decreases the melting and reduction speeds.

The object of the invention is attained also by providing a furnace forthe realization of the method, comprising a melting pot with a hearth, astack resting on the melting pot and having at least one device forloading the iron-bearing material and solid carbon fuel into the meltingpot, said device located in the upper part of the stack, tuyeres withnozzles for delivering the oxygen-containing gas into the melting potwhich has a slag discharge channel made in the wall of the melting potat its hearth, and a channel for discharging the ferrocarbonintermediate product made in the wall of the melting pot below theinstallation level of tuyeres with nozzles, and a device for dischargingthe process gases, located in the upper part of the stack wherein,according to the invention, the horizontal sections of the melting potand stack have, essentially, a rectangular shape, the tuyeres withnozzles are installed in the upper portion of the longer walls of themelting pot, the slag discharge channel and the channel for thedischarge of ferrocarbon intermediate product are made in the shorterwalls of the melting pot, the ratio of the horizontal section area ofthe melting pot at the installation level of the tuyeres with nozzles tothe total area of the tuyere outlet orifices being 300 to 10000, and thedistance from the lower boundary of the channel for discharging theintermediate product to the upper boundary of the slag discharge channelis 0.3 to 0.75 of the distance from the lower boundary of theintermediate product discharge channel to the installation level oftuyeres with nozzles in the melting pot.

The furnace for the production of ferrocarbon intermediate product foruse in steel manufacture comprises a melting pot with a hearth, a stackresting on the melting pot and provided with at least one device forloading the iron-bearing material and solid carbon fuel into the meltingpot said device being located in the upper part of the stack, tuyereswith nozzles for feeding the oxygen-containing gas into the melting potwhich is provided with a channel for discharging the ferrocarbonintermediate product made in the melting pot wall below the tuyereinstallation level and a slag discharge channel made in the melting potwall at its hearth, and a device for discharging the process gases fromthe stack located in its upper part, the melting pot and the stackbeing, essentially, of a rectangular shape in the horizontal section,tuyeres with the nozzles are installed in the upper portion of thelonger walls of the melting pot so that the ratio of the horizontalsection of the melting pot at the installation level of the tuyeres withnozzles to the total area of the nozzle outlet orifices is 300 to 10000and the channels are made in the shorter walls of the melting pot sothat the distance from the lower end of the product discharge channel tothe upper end of the slag discharge channel is 0.3 to 0.75 of thedistance from the lower boundary of the product discharge channel to thetuyere installation level in the melting pot.

Realization of the melting pot and stack of the rectangular shape in thehorizontal section and location of the tuyeres with nozzles for thedelivery of the oxygen-containing gas into the melt on itscounteropposed longer side walls to face each other ensures theconditions for an intensive stirring of the melt throughout its volumeand, in addition, makes it possible to increase the furnace capacity byincreasing its length at a constant width. Intensive stirring ensureshigh speeds of oxidation of solid carbon fuel, of melting of theiron-bearing material and reduction of metal oxides from slag and,consequently, optimum process characteristics i.e. high furnace outputand low fuel consumption.

The arrangement of the tuyeres with nozzles in the upper portion of themelting pot walls makes it possible to create a zone of quiescent meltin the lower portion of the melting pot.

The ratio of the horizontal section area of the melting pot at theinstallation level of the tuyeres with nozzles to the total area of thenozzle outlet orifices exceeding 10000 results in a low bubblingintensity or in the need for resorting to excessively high feedvelocities and pressure of the oxygen-containing gas which impairs theperformance of the tuyeres and raises the cost of power-engineeringequipment. The ratio below 300 is not expedient due to formation of anexcessively large volume of oxidizing zones in the melt, which resultsin a reduced speed of reduction and a danger of melt throwout, and alsodue to the necessity of using low speeds of discharge of theoxygen-containing gas into the melt, which may bring about flooding ofthe nozzles with the melt.

Arranging the channels in the opposite shorter walls of the melting potand the above-specified distances from the lower boundary of the channelfor discharging the metal--intermediate product--to the upper boundaryof the slag discharge channel ensure optimum conditions for theseparation of metal and slag, prevent losses of solid carbon fuel andmetal with slag, thus making it possible to increase the extraction ofmetal and reduce the consumption of solid carbon fuel. When the distancebetween the lower boundary of the metal discharge channel and the upperboundary of the slag discharge channel is smaller than 0.3 of thedistance from the lower boundary of the metal discharge channel to theinstallation level of the tuyeres with nozzles, the slag dischargechannel will be accomplished directly above the layer of metal. Thiswill cause the absence of a slowly replaceable slag layer above themetal and a reduction in the process stability fluctuations in thechemical composition of slag in the upper bubbled zone. When thedistance from the lower boundary of the metal discharge channel to theupper boundary of the slag discharge channel is larger than 0.75 thedistance from the lower boundary of the metal discharge channel to thetuyere installation level, particles of solid carbon and metal drops arecarried out with slag, which increases the consumption of solid carbonfuel and cuts down the furnace output.

All the above-listed measures taken together make for a high outputcombined with absolute reliability of the furnace, improve theseparation of metal, i.e. intermediate product, for use in steel andslag manufacture and ensure a high percentage of metal extraction fromthe raw material being processed at a lower consumption of carbon fuel.

With a view to reducing the consumption of refractories and extendingthe duration of furnace interrepair periods, it is expedient that theupper part of the melting pot and at least the lower part of the stackbe made cooled. If so, the cooled surfaces become covered with slagcrust, which contributes to a reduction of heat losses.

The tuyeres with nozzles for the delivery of the oxygen-containing gasinto the melting pot should better be installed in the cooled part ofthe melting pot, since above the tuyere axes and somewhat lower thereappears a bubbled melt zone, wherein the corrosive slag laden with solidparticles of fuel and iron-bearing material moves intensively, washingthe furnace walls.

A substantial advantageous feature also consists in that the furnacecomprises a slag precipitation vat with a slag discharge holecommunicating with the melting pot through its slag discharge channel,the average area of the horizontal section of the slag precipitation vatbeing 0.03 to 0.3 the average horizontal section area of the meltingpot.

The provision of the slag precipitation vat provides for a finerseparation of slag and small droplets of metal. The attendant increasein the path of the slag to the point of discharge from the furnace andlow speeds of lifting the slag to the reservoirs for its dischargefavour the coalescence precipitation of metal drops from the slag. Ifthe average horizontal section area of the slag precipitation vat issmaller than 0.03 the average horizontal section area of the meltingpot, the rate of precipitation of metal drops is lower than the speed ofslag lifting into the precipitation reservoirs, so that in this casethere is no reduction of losses of metal with the discharged slag. Theaverage horizontal section area of the slag precipitation vat largerthan 0.3 the horizontal section area of the melting pot does not bringabout further reduction of metal losses with slag but leads tosupercooling of the latter, hinders its discharge or steps up theconsumption of fuel spent for superheating the slag in the furnace orfor its heating in the precipitation reservoir.

The vertical distance from the melting pot hearth to the lower edge ofthe hole in the slag precipitation vat should better be set within 1.1to 2.5 the distance from the melting pot hearth to the installationlevel of the tuyeres with nozzles in it.

All other conditions being equal, the relation of said distances governsthe relation between the heights of the bubbled and quiescent zones ofthe slag melt.

When the distance from the level of the melting pot hearth to the loweredge of the hole in the slag precipitation vat are less than 1.1 thedistance from the hearth to the installation level of the tuyeres withnozzles, the height of the quiescent zone and, consequently, thethickness of the quiescent layer of slag will be small. This will impairthe separation of metal from slag and the refining of metal, forexample, from sulphur. The maintenance of the sulphur content at apresent level will call for raising the basicity of slag by increasingthe flux consumption and, as a consequence, will raise the fuelconsumption and reduce the output. At distances from the melting pothearth to the lower edge of the hole in the slag precipitation vatexceeding 2.5 the distance from the hearth to the installation level oftuyeres with nozzles the thickness of the quiescent layer of slag grows.However, this does not improve further the refining of metal and doesnot reduce metal content in the discharged slag; instead, it reduces thetemperature of metal and increases heat losses.

To achieve reliable continuous output of the intermediate product andstabilize its level in the melting pot, it is practicable that thefurnace have a reservoir for settling of the intermediate product with ahole for its discharge communicating with the melting pot through achannel for discharging the product therefrom.

In the absence of such a reservoir the product may be discharged eitherperiodically or continuously through a calibrated channel which providesfor a constant speed of metal outflow. However, in this case there is aneed for sophisticated facilities for shutting down the channel underpressure. It is difficult to maintain a constant cross section of thechannel in the direction of metal discharge and still more difficult toadjust the channel cross section for changing the metal discharge uponchanges in the furnace output or when it is necessary to change themetal level in the melting pot. Thus, the furnace wherein the metal isdischarged through a calibrated channel is insufficiently reliable. If areservoir has a metal discharge hole, the metal is drained withoutpressure over the threshold of said hole. The metal level in the meltingpot can be adjusted by changing the level of the threshold of the holedischarging metal from the reservoir.

This ensures reliable maintenance of the melt level in the furnace,higher flexibility of its adjustment and elimination of emergencysituations. The result is stabilization and flexible governing of theprocess which, in the long run, steps up the output.

It is practicable that the upper part of the stack should be providedwith at least one horizontal row of additional tuyeres for feedingoxygen-containing gas into the melting pot.

This method of tuyere installation permits the oxygen-containing gas tobe fed for reburning the combustible gases emitted from the bubbled meltand ensures utilization of the heat of gases directly in the furnace.The immediate result is a lower fuel consumption and a higher output.The tuyeres installed in more than one row along the horizontalcontribute to uniformity of reburning.

It is deemed expedient that the distance from the melting pot bearth tothe installation level of the additional tuyeres of any row in the upperpart of the stack should be 1.5 to 6.0 the distance from the melting pothearth to the installation level of the main tuyeres in said pot. If thedistance from the of the melting pot to the additional tuyeres forfeeding the oxygen-containing gas above the upper zone of the bubbledmelt is less than 1.5 the distance from the melting pot hearth to theinstallation level of main tuyeres this leads to oxidation of solidcarbon fuel from the bath with the oxygen-containing gas delivered forreburning. In this case the melt bath may be superoxidized. This willstep up the consumption and reduce the output.

If the distance from the hearth of the melting pot to the additionaltuyeres for feeding the oxygen-containing gas above the upper zone ofthe bubbled melt is less than 6.0, the distance from the melting pothearth to the installation level of the main tuyeres with nozzles forfeeding the oxygen-containing gas into the melt, this provesinexpedient, since the flame of the burning gases emitted from the bathwill be located too high above the melt surface. This impairs heattransfer to the bath and reduces the efficiency of the process.

It is expedient that the horizontal section area of the stack at theinstallation level of the additional tuyeres of any row should be 1.05to 2.0 the horizontal section area of the melting pot at theinstallation level of the main tuyeres with nozzles feeding theoxygen-containing gas into the melt.

Heat transfer from the reburning zone to the melt preceeds in two ways,i.e. by radiation of the flame jet to the melt and by convection, mostlydue to heating of the metal sphlashes flying from the melt bath to thereburning zone. The amount of heat received by the melt due to radiationdepends on the area of projection of the surface of the bubbled melt onthe horizontal surface while the amount of heat transferred byconvention depends on the mass and flying height of the sphlashes whichdepend on the specific intensity (per unit area) of gas dischargethrough the melt surface.

As a consequence, when the cross-sectional area of the stack at theinstallation level of additional tuyeres exceeds 2.0 the horizontalsection area of the melting pot at the installation level of the maintuyeres, there is no further imporvement of heat transfer by radiation;besides, the heat transfer by convection is reduced. In addition, anincrease in the surface area of the walls results in higher heat losses.As a result, the total amount of heat received by the bath due toreburning is reduced.

When the horizontal section area of the stack at the installation levelof additional tuyeres for feeding the oxygen-containing gas above thelevel of the upper zone of slag melt is less than 1.05 the horizontalsection area of the melting pot at the installation level of the maintuyeres with nozzles for the delivery of the oxygen-containing gas intothe melt there is no heat transfer by convection but the heat transferby radiation is reduced due to a disminished area of the surface of thebubbled melt: besides complete reburning directly above the surface ofthe bubbled melt is also reduced. Thus, when the above-specified limitsare violated, the furnace output drops while specific consumption ofsolid carbon fuel grows.

It is expedient that at least the lower part of the stack in itsvertical cross section be made in the form of a trapezium whose smallerbase rests on the melting pot.

In the course of bubbling the melt level rises and its upper zone, whichis a gas-liquid system, is situated in the lower part of the stack. Ifthe stack at this point has the shape of a tropezoid with its smallerbase facing down, this increases the area of the surface of the bubbledmelt. As a result, the surface area receiving the heat transferred byradiation from the reburning zone increases. Besides, the volume of thereburning space in the stack increases too. This ensures advantageousconditions for mixing the oxygen-containing gas with the combustiblegases envolved from the melt and for reburning said gases directly abovethe melt with a higher degree of completeness.

BRIEF DESCRIPTION OF DRAWINGS

Now the invention will be made more apparent by referring to itsspecific embodiments and the accompanying drawings, in which:

FIG. 1 is a schematic general view of a furnace for the preparation offerrocarbon intermediate product use in steelmaking (transverse verticalsection), according to the invention;

FIG. 2 is a view along line II--II in FIG. 1;

FIG. 3 is a view along line III--III in FIG. 2;

FIG. 4 is a general view of a furnace for preparation of ferrocarbonintermediate product for use in steel manufacture, provided with a slagprecipitation vat (longitudinal vrtical section), according to theinvention;

FIG. 5 is a general view of a furnace for preparation of ferrocarbonintermediate product for use in steel manufacture, provided with a slagprecipitation vat and an intermediate product precipitation vat(longitudinal vertical section), according to the invention;

FIG. 6 is a general view of a furnace for preparation of ferrocarbonintermediate product for use in steel manufacture provided withadditional tuyeres for the delivery of oxygen-containing gas (verticaltransverse section), according to the invention;

FIG. 7 is a view along line VII--VII in FIG. 6.

THE BEST WAY OF CARRYING THE INVENTION INTO EFFECT

The hereinproposed method for the preparation of ferrocarbonintermediate product for use in steel manufacture comprises thefollowing technological operations.

The furnace is charged simultaneously with iron-bearing material 1(FIG. 1) and solid carbon fuel 2. Concurrently with charging, thefurnace is fed with oxygen-containing gas 3 whose oxygen oxidizes partof fuel 2 accompanied by liberation of heat. This liberated heat meltsiron-bearing material 1 and the metal oxides it contains are reuced bythe carbon of the remaining part of fuel 2 forming liquid meltingproducts, i.e. slag 4 (FIG. 2) and ferrocarbon intermediate product 5.

Then the slag 4, intermediate product 5 and process gases 6 formed inthe course of melting are discharged from the furnace.

According to the invention, concurrent charging of the iron-bearingmaterial 1 and solid carbon fuel 2 is preceded by building up slag melt.This is done by pouring in liquid slag produced in the manufacture offerrous metals, for instance, in electric furnaces.

In another embodiment, the beginning of melting process is speeded upand the wear of the lining is reduced by pouring in liquid metal beforepouring in slag, the liquid metal being poured higher than its dischargelevel but lower than the slag discharge level. The liquid may be eithercast iron or some other ferrocarbon melt.

In a third embodiment resorted to in the absence of liquid slag the slagmelt is built up by loading solid oxide materials into the furnace andmelting them therein. The solid oxide materials may be represented byslags produced in the manufacture of ferrous metals (blast furnace,converter, open hearth, electric furnace slags, etc.), minerals(dolomite, limestone, sand, spar, etc.), metal oxides (CaO, MgO, SiO₂,Al₂ O₃, etc.). These materials may belong to any one of the mentionedgroups or to some of them simultaneously.

Then oxygen-containing gas 3 is fed into the built up melt, below itssurface level. The oxygen-containing gas 3 can be either commercialoxygen (99.5% O₂) commercial oxygen (95% O₂), or oxygen-enriched air.

The stream 7 (FIG. 1) of oxygen-containing gas 3 divides the melt intotwo zones, viz., lower zone 8 of the quiescent melt and upper zone 9 ofthe melt bubbled with gas 3.

To simplify the subsequent discussion the term "lower quiescent zone 8"of the melt and "upper bubbled zone 9" of the melt will be used.

Then the upper bubbled zone 9 is loaded with solid carbon fuel 2 in anamount sufficient for building up a volumetric concentration of fuelwithin 0.5 to 50% of the total melt volume in said zone. These limitsare selected on the one hand due to the necessity for oxidizing the fuel2 in the melt with the oxygen-containing gas 3 and forming CO and, onthe other hand, with a view to preserving the flowability of the melt. Aspecific value of the concentration is determined by taking in accountthe amount of the delivered oxygen-containing gas, the properties ofslag 4, the type and properties of the solid carbon fuel, and otherparameters of the process.

Further on, the concentration of solid carbon fuel is maintained bysimultaneous charging of the upper zone 9 with the iron-bearing material1 and solid carbon fuel 2.

The solid carbon fuel may be constituted by various kinds ofcarbon-containing materials, preferably coal. Alternative fuels arebrown coal, peat, charcoal, coke byproducts, schungite, shale,anthracite, products of pyrolysis of carbon-containing organic materialsand carbon-bearing waste (plastics, rubber, etc.).

The processed iron-bearing material may be iron ore, iron-oreconcentrate and iron-ore raw materials reduced to various extents(sponge iron). The method proves effective in processing dried slimes,dust formed in dry gas purifiers of metallurgical industry, scale,including oiled scale. Also possible is remelting of fine steel and castiron scrap, particularly chips.

The bubbled zone 9 created by injection of oxygen-containing gas 3 intothe melt and by subsequent loading it with solid carbon fuel 2 andiron-bearing material 1 is a complicated heterogeneous system comprisingslag melt, gaseous phase, particles of solid carbon fuel, particles ofsolid iron-bearing material, drops of molten iron-bearing and drops ofmetal--intermediate product--obtained by reduction of metal oxides fromthe slag metal. This system is mixed by the energy of the injectedoxygen-containing gas 3 delivered in the amount of 150 to 1500 Nm³ /hper m² of the horizontal section area of the melt at the delivery levelof the oxygen-containing gas 3 according to the type of fuel, propertiesof the slag melt, oxygen content in the oxygen-containing gas, desiredoutput, etc.

The flow rate of the oxygen-containing gas 3 delivered into the melt isincreased when the reactivity of the solid carbon fuel 2 increases.

The result is the interaction of the iron-bearing material 1, solidcarbon fuel 2 and oxygen-containing gas 3 accompained by the formationof liquid slag 4 and liquid metal, i.e. ferrocarbon intermediate product5 used in steel manufacture.

In the bubbled zone 9 of the melt the oxygen-containing gas 3 interactswith the carbon of the solid carbon fuel 2. ##EQU1##

The interaction yields energy necessary for preparation of ferrocarbonproduct 5 from the iron-bearing material 1.

To improve the functioning of the injection devices, to speed up theinteraction of the oxygen contained in the oxygen-containing gas 3 withthe fuel 2, to reduce the volume of the gas oxidizing zones in the melt4 and to improve the thermal coditions the bubbled zone 9 of the melt isadditionally fed, under the melt surface, with liquid, gaseous or solidpulverized carbon-containing fuel. The gaseous, liquid or pulverizedsolid carbon-containing fuel is best delivered jointly with theoxygen-containing gas. This contributes to efficient mixing and burningof the fuel within a short portion of the one of fuel delivery into themelt.

The iron-bearing material 1 in a cold or preliminarily heated stateenters the bubbled zone 9 and is assimilated with the slag melt whereinit is heated and melted. The metal component of the iron-bearingmaterial 1 forms metal drops which descend into the lower quiescent zone8 of the melt, forming a layer of metal i.e. ferrocarbon intermediateproduct 5 for use in steel manufacture or continuously replenishing thislayer. Melting, the oxide component of the iron-bearing materialdissolves in the slag of the bubbled zone 9, thus increasing the contenttherein of the oxides of iron, manganese, silicon, etc.

The oxides of iron and other metals, e.g. silicon, manganese nickel,chromium, etc. are reduced from the slag melt by the carbon of the solidcarbon fuel. ##EQU2##

The metal drops formed through reduction are coagulated and descend bygravity in the quiescent zone 8 through the layer of slag 4 into themetal layer 5.

The layer of slag 4 in the quiescent zone 8 is renewed by the slag meltflowing from the bubbled zone 9.

Thus, the quiescent zone 8 consists of an upper layer of slag 4 and alower layer of metal 5.

The liquid products of melting, i.e. metal, (ferrocarbon intermediateproduct 5) and slag 4 are discharged separately from the correspondinglayers of the calm zone 8. The metal 5 is discharged from the lower partof its layer. Slag 4 can also be discharged from the lower part of theslag layer. However, for a better stability of the process, the slag 4is discharged from the middle or upper parts of its layer in thequiescent zone 8.

As the drops of metal 5 interact with the slag 4, the metal is refinedfrom impurities (sulphur, phosphorus). The chemical composition of slag4 is adjusted by loading fluxed additions into the bubbled zone 9. Asdistinct from the blast-furnace melting, the composition of slag mayvary within wider limits, which improves its refining property andproduces a purer metal.

The main part of su lphur introduced mostly with the solid carbon fuelcan be removed with the discharged gases 6 in the form of gaseouscompounds (COS, H₂ S, etc.). For a better removal of sulphur into thegaseous phase and for producing a low-sulphur metal, theoxygen-containing gas 3 is fed into the melt in the course of meltingcontinuously, periodically stopping the concurrent loading of theiron-bearing material 1 and solid carbon fuel 2. It provides forperiodic additional refining from sulphur of the slag melt in thebubbled zone 9, thereby raising its sulphur absorbing capacity.

The gases 6 evolved in the bubbled zone 9 are liberated from the meltand discharged from the furnace. These gases 6 consist chiefly of CO andH₂, their temperature approaching that of the melt. They can be used asa gaseous fuel or as a process reducing gas, for example for directproduction of iron or for injection into blast furnaces.

However, when reducing gas is produced as a result of melting, this isaccompained by the release of a comparatively small amount of heat.Therefore, to obtain a sufficiently high efficiency of the method forpreparing ferrocarbon, product, the iron-bearing material shouldpreferably be respresented by previously reduced iron-ore raw materialsor small-size metal scrap.

The additional feed of the oxygen-containing gas 3 above the level ofthe bubbled melt zone 9 ensures a more effective utilization of theenergy of the solid carbon fuel, as well as of the liquid, gaseous orsolid pulverized carbon-containing fuel directly in the process forpreparing the ferrocarbon intermediate product. In this case the CO andH₂ liberated from the melt are reburned partly or completely to CO₂ andH₂ O:

    CO+1/2O.sub.2 =CO.sub.2

    H.sub.2 1/2O.sub.2 =H.sub.2 O.

The heat released by these exothermic reactions heats the slag in thebubbled zone 9 and is spent for melting the iron-bearing material 1 andreducing the oxides of its metals. The additional heat permits raisingthe efficiency of the process or using the iron-ore raw materialswithout preliminary reduction, at the same time retaining the highoutput.

During complete reburning of the gases released from the melt in thecourse of melting, only noncombustible gases are produced anddischarged. This simplifies substantially the utilization of theirenergy, since effective utilization of the sensible heat of gases can beachieved by far easier than by the use of their chemical heat.

The oxygen-containing gas 3 delivered above the level of the bubbledzone 9 of the melt is constituted by commercial oxygen (95% O₂), or airenriched with commercial oxygen, or air as such.

The oxygen-containing gas 3 delivered above the level of the bubbledzone 9 of the melt is delivered at the rate of (0.01 to 5.0)×10³ Nm³ pert of solid carbon fuel depending on the chemical composition of thesolid carbon fuel, oxygen content in the oxygen-containing gas, therequisite degree of reburning, etc.

In the course of concurrent loading of solid carbon fuel 2 andiron-bearing material 1 the fuel is loaded at the rate of 0.2 to 0.5 t/hper m² of the horizontal section area of the melt at the level ofdelivery into it of the oxygen-containing gas 3. The amount of fuel isselected on the basis of the flow rate of the oxygen-containing gasdelivered into the melt, the oxygen content is said gas, the chemicalcomposition of the solid carbon fuel and the degree of reburning. Highvalues are characteristic of the fuel with a low carbon content also ofmelting the iron-ore raw materials at high degrees of reburning of thegases discharged from the melt.

The hereinproposed method is realized in the best possible way by meansof the hereinproposed furnace comprising a melting pot 10 (FIG. 1 and 2)with hearth 11, stack 12 resting on top of said melting pot 10, tuyeres13 with nozzles 14 (FIG. 2) delivering the oxygen-containing gas 3 intothe melting pot 10 and a means 15 in the top part of the stack fordischarging the process gases 6 from the furnace. Besides, stack 12 isprovided with at least one device 16 for charging the iron-bearingmaterial 1 and solid carbon fuel 2 into the melting pot 10. The meltingpot 10 has a channel 17 for taking out slag 4, said channel made in thewall of the melting pot 10 at its hearth 11, and a channel fordischarging the metal, i.e. ferrocarbon intermediate product 5 referredto hereinafter simply as "metal" 5, said channel being also made in thewall of the melting pot 10 below the installation level of tuyeres 13.

According to the present invention the melting pot 10 and stack 12 aresubstantially rectangular in the horizontal section. The upper part ofthe melting pot 10 and at least the lower part of the stack 12 havecooling elements 19. The cooling agent is either water or some othersimilar heat-transfer agent. The tuyeres 13 (FIG. 3) with nozzles 14 forthe delivery of oxygen-containing gas into the melting pot 10 areinstalled in its upper cooled part on the opposite longer sides of thepot 10, facing each other. The ratio of the horizontal section area ofthe melting pot 10 at the installation level of tuyeres 13 and nozzles14 to the total area of the outlet orifices of nozzles 14 ranges from300 to 10000.

These limits permit the oxygen-containing gas to be delivered into themelt at a flow rate proposed in the present method for preparing theferrocarbon product at optimum velocities which ensure, on the one hand,efficient stirring of the melt and, on the other hand, high stabilityand reliability of tuyeres 13 and nozzles 14.

The slag discharge channel 17 is made in one of the shorter wall of themelting pot 10, while the channel 18 for the discharge of theintermediate product is made in the opposite shorter wall of the pot 10,at its hearth 11.

The distance h from the lower boundary of the metal-discharge channel 18to the upper boundary of the slag discharge channel 17 is 0.3 to 0.75the distance H from the lower boundary of the channel 18 to theinstallation level of tuyeres 13 with nozzles 14 in the melting pot 10.The installation level of tuyeres 13 is measured from the surface of thehearth 11 to the longitudinal geometrical axes of tuyeres 13.

At the above-mentioned ratio the slag is discharged from optimal levelsalong the height of its layer. This ensures, on its one hand, presenceof a slowly replaceable slag over the metal, this contributing to anincrease in the process stability when the degree of slag oxidation inthe bubbled zone is increased, and, on the other hand, precluding lossesof particles of solid carbon fuel and metal slags with the slag beingdischarged.

The furnace comprises also a slag precipitation vat 20 (FIG. 4) with ahearth 21, said vat having a hole 22 for discharging slag into the slagpot (not shown in the Figure) and communicating with the melting pot 10through the channel 17. This design of the furnace and the provision ofthe vat 20 makes it possible to discharge the slag continuously as it isformed. The threshold of the discharge hole 22 defines the level of themelting bath in the furnace. By changing the height of the threshold onecan change the melt level in the furnace.

The average horizontal section area of the vat 20 is 0.03 to 0.3 theaverage horizontal section area of the melting pot 10.

Such values of the average horizontal section area of the vat 20 withrelation to the average horizontal section area of the melting pot 10provide for effective separation of small droplets of metal 5 from slag4 in the pot 10.

The hearth 21 of the vat 20 is made level with the hearth 11 of themelting pot 10. The lower level of the channel 17 coincides with thelevel of hearths 11 and 21. As a result, the metal drops 5 separated inthe vat 20 from slag 4 accumulate in a layer on the hearth 21, and metal5 returns into the melting pot 10 through channel 17.

The vertical distance H₁ from the level of the hearth 11 to the loweredge of the discharge hole 22 is 1.1 to 2.5 the distance H₂ from thelevel of the hearth 11 to the installation level of tuyeres 13 withnozzles 14 in the melting pot 10. The distances H₁ and H₂ are equal whenthe metal discharge channel 18 is located at the hearth 11 of themelting pot 10. This ensures optimum relationships between the heightsof the bubbled zone and calm zone 8 of the melt and, consequently, theoptimum height of the layer of clam slag 4 at which said layer allowsfor effective separation of metal drops and their refinement fromimpurities without imparing the heat transfer to the metal layer abdwithout increasing heat losses.

To ensure reliable and continuous discharge of metal and to stabilizethe metal level in the furnace, the latter is fitted at the end sidewith an external vat 23 (FIG. 5) for precipitation of the intermediateproduct, i.e. metal 5, said vat communicating with the melting pot 10through the metal discharge channel 18. The vat 23 has a hearth 24arranged level with the hearth 11 of the melting pot 10. The vat 23 hasa hole 25 for discharging metal into the ladle (not shown in thedrawing) whose threshold level determines the height of the metal layer5 in the quiescent zone 8 of the melt in the melting pot 10.

In order to utilize the energy of combustible process gases 6 evolvedfrom the melt for improving its thermal efficiency and the utilizationeffect of the solid carbon fuel, the furnace is equipped with additionaltuyeres 26 (FIG. 6) with nozzles 27 for feeding the oxygen-containinggas into the melting pot 10 above the level of the bubbled zone 9 of themelt. The tuyeres 26 are arranged in one or more rows along the heightof the stack 12 in arches 28 made in its longer walls. The tuyeres 26are installed with a provision for moving along their axes into thestack over a distance of up to 0.5 of its width at the point ofinstallation of the tuyeres 26 and with a provision for changing theinclination angle of the tuyere axes from 0° to 60° to the horizontal.The tuyeres 26 are moved into the stack 12 and the angle of the tuyeres26 to the horizontal is changed by special mechanical means (not shownin the Figure).

To ensure high degrees of reburning and efficient heat transfer from theflame jet to the melt and to prevent burning the solid carbon fuel bythe oxygen-containing gas delivered above the level of the bubbled zone9 of the melt, also to prevent overoxidation of the melt the tuyeres 26(FIG. 7) are installed at a distance H₃ from the hearth 11, equal to 1.5to 6.0 the distance H₂ from the hearth 11 to the installation level ofthe main tuyeres 13 with nozzles 14.

The installation level of the additional tuyeres 26 depends on theposition of the lower edge of the outlet holes of the nozzles 27 inrelation to the hearth 11.

For delivering oxygen-containing gas above the level of the bubbled zone9 operating with reburning of the process gases in order to improve theheat transfer by radiation from the jet flame to the melt and thus toincrease the utilization degree of the reburning heat, the lower part 29of the stack 12 in the furnace with tuyeres 26 (FIG. 5) has the form ofa trapezoid in the vertical cross-section, the smaller base of saidtrapezoid resting on the melting pot 10. The trapezoidal shape providesfor widening the melting bath, for increasing the projection area of themelt surface in the bubbled zone 9 in the horizontal plane, and forincreasing the stack volume above the melt in the reburning zone. Themiddle portion of the stack and the whole stack may also have atrapezoidal shape.

To increase the total degree of utilization of the reburning heat byoptimizing the heat transfer by radiation and convection from the flamejet to the melt, the horizontal section area of the stack at theinstallation level of additional tuyeres 26 for feedingoxygen-containing gas above the level of the bubbled zone 9 of the meltis 1.05 to 2.0 the horizontal section area of the melting pot 10 at theinstallation level of the main tuyeres 13 with nozzles 14 for deliveryof oxygen-containing gas to the melt. Within the above-specified limitsthe concrete value is selected on the basis of the flow rate of theoxygen-containing gas delivered into the melt, the degree of reburning,height of the melting bath and geometrical dimensions of the furnace.

The furnace for realizing the method for preparing the ferrocarbonintermediate product functions as follows.

To build up a slag melt, the melting pot 10 with a previously heatedrefractory lining is filled with liquid slag obtained as a byproduct ina blast furnace or an openhearth furnace or, else, in an electric steelmelting furnace or with liquid synthetic slag first melted, for example,in a slag melting electric furnace. The slag is poured in to the leveldisposed above the installation level of the tuyeres 13 with nozzles 14.If the vat 20 is used, the maximum pouring-in level corresponds to thethreshold level of the hole 22 for discharging slag from the vat 20.

In another embodiment before pouring slag into the furnace the latter isfilled with liquid metal, preferably cast iron, to the level higher thanthe upper boundary metal discharge channel 18 but lower than the lowerboundary of the slag discharge channel 17.

In the third method of building up slag melt the hearth 11 of the heatedfurnace is loaded with solid oxide materials, viz., crushed slagsproduced in the ferrous metal manufacture, mineral raw materials, metaloxides, and said materials are melted. The solid oxide materials aremelted until the slag level in the furnace rises above the installationlevel of tuyeres 13 with nozzles 14.

If it becomes impossible for some reason to fill the furnace completelywith liquid slag above the level of tuyeres 13 with nozzles 14, theavailable amount is poured in and the bath is subsequently built up withsolid oxide materials. Having built up the slag melt, anoxygen-containing gas is fed into it, under the surface, through tuyeres13 with nozzles 14 and, if need be, liquid, gaseous or solid pulverizedcarbon-containing fuel under a pressure exceeding the static pressure ofthe slag melt column above the tuyeres 13, at a consumption rate of150-1500 Nm³ /h per m² of the horizontal section area of the bath at theinstallation level of tuyeres 13 with nozzles 14.

Thus, the melt is divided into two zones, the upper bubbled zone 9 andthe lower quiescent zone 8. When the upper zone 9 of the slag melt ishigher and somewhat lower than the axes of tuyeres 13 with nozzles 14,it begins mixing intrensively, being turned into a gas-liquid system.

Then the melt is loaded from above through device 16 with solid carbonfuel 21, for example lump coal, with practically no limitations on thesize of lumps because, due to a thermal shock in the bath and liberationof volatile components, the coal is disinegrated into practicles 3 to 4mm in size, maximum. Other kinds of solid carbon fuel are used in themilled state.

The particales of solid carbon fuel 2 loaded into the bubbled melt ofthe upper zone 9 are distributed throughout the volume of the melt. Thevolumetric concentration of fuel is brought to 0.5 to 50% of the meltvolume in the zone 9. Entering the tuyere zones, the particles of fuel 2interact with the oxygen-containing gas, forming carbon monixide.

Due to the heat released through oxidation of fuel, the melt bath isheated to 1450° to 1650° C. Then solid carbon fuel 2 and iron-bearingmaterial 1 begin to be concurrently loaded into the upper zone 9 of thebubbled melt through device 16. Meanwhile the volumetric concentrationof solid carbon fuel 2 in the bubbled zone 9 of the melt is maintainedwithin the same limits (0.5 to 50% of the melt volume in said zone).

On condition of ensuring sufficient output, the iron-bearing material 1for preparing ferrocarbon product is constituted, for the processwithout reburning the process gases in the furnace by the materialscontaining mostly metallic iron (iron-ore raw materials (sponge iron)reduced in advance, small-size steel or cast iron scrap, chips; for theprocess with reburning, oxidized materials (iron ore, iron-oreconcentrate, dust produced at gas-purifying works, dried slime).

For producing alloyed ferrocarbon product the charge is mixed with rawmaterials containing alloying elements (manganese, nickel and other oresand concentrates thereof).

Besides, in order to produce slag of a desired composition, the chargeis mixed with fluxing additions of which the most common one is lime,through it can be substituted by crude limestone.

The iron-baring materials, alloying and fluxing additions, as well assolid carbon fuel, are loaded concurrently into the furnace throughcharging device 16.

The charge is delivered to the device 16 either mixed or by separatecomponents by a belt conveyor (not shown in the Figure).

A large furnace may have several charging device 16.

As the charge materials fall into the melt, they become quickly anduniformly spread throughout the volume of its upper bubbled zone 9 dueto mixing of the melt. A high intensity of melt movement, dispersiontherein of the energy sources and uniform distribution of the chargematerials provide favourable prerequisites for fast heating and meltingof the iron-bearing material and additions. The permissible lump size ofthe iron-bearing material and additions depends on their properties, theproperties of the slag, intensity of delivery of the oxygen-containinggas into the melt, the temperature of the process and may reach 20 to 30mm.

Being melted, the metallic component of the iron-bearing material 1forms, metal drops while the oxide component gets dissolved in the slag.The oxides, of iron and some other materials (Si, Mn, Cr, Ni, etc.) arereduced by the oxygen of the solid carbon fuel 2, forming metal drops.

The small metal droplets may stay for quite a long time in the bubbledzone 9. Here a stationary concentration of said droplets sets in, saidconcentration depending on the velocity of melt motion. As thisconcentration rises, the droplets coagulate, grow in size and alreadycannot stay in the upper bubbled zone 9. They sink into the lowerquiescent zone 8, passing through the layer of quiescent slag 4 and jointhe layer of metal 5 on the hearth 11.

The large drops of metal formed by melting of the metal component of theiron-bearing material quickly precipitate from the upper bubbled zone 9.The melt temperature in the upper bubbled zone is higher than that inthe lower quiscent zone 8. Heat enters the lower quiescent zone 8 mostlywith the drops of metal 5 which get heated in the upper bubbled zone 9.

Owing to the high temperature in the upper bubbled zone 9 and the largeboundary surface between the reacting phases, i.e. gas--solidcarbon--liquid slag-metal the metal oxides become reduced at a highspeed. As a result, the efficiency of the process is restricted, as arule, not by the reduction kinetics, but by the supply of heat. Thecorrosive melt in the upper bubbled zone 9 and somewhat above contactsthe cooling elements 19. Said elements 19 become covered with a layer ofslag crust 5-25 mm thick, which averts large heat losses and protectsthem against abrasive attrition by the particles of solid carbon fuel 2and iron-bearing material 1 contained in the upper bubbled zone 9 of theslag melt.

The melt of the lower part of the melting pot 10 where metal 5 and slag4 come from the upper bubbled zone 9 contacts with the refractorybrickwork. However, slag in this zone is considrably less corrosivesince it already contains no solid articles, has a lower content of ironoxides and a low velocity of movement. Therefore the refractories inthis zone are sufficiently stable.

A low velocity of the slag in the quiescent zone 8 provides favourableprerequisites for the precipitation of metal drops therefrom. This isaccompanied by additional refining of metal drops from impurities.

The slag 4 is discharged from its layer in the quiescent zone 8 throughchannel the 17 in the end wall of the melting pot 10. By changing theheight from the hearth 11 to the upper boundary of the channel 17 onecan discharge slag from different heights of its layer. When the slag isdischarged from the lower portion of its layer, this ensures a somewhatbetter separation of the metal drops from slag inside the melting pot10. However, in this case the layer of slag directly adjoining the layerof metal is continuously renewed in the course of melting which maybring about a temporary increase in the oxidation state of slag in thelower quiescent zone 8 and may cause the metal to boil. This may affectadversely the stability of the process and of the refractory lining ofthe melting pot 10.

These phenomena are prevented by discharging the slag from the middle orupper parts of its layer in the quiescent zone 8. In this case there isan extremely slowly renewed layer of liquid slag on top of the liquidmetal with an equilibrium content of iron oxides relative to the carboncontent in metal.

The provision of slag precipitation vat 20 diminishes actually thelosses of metal 5 with slag 4. Passing through the channel 17, slag 4enters the lined vat 20 and proceeds moving upward. Owing to arelatively large horizontal section of the vat 20 the velocity of slagflow diminishes thus enabling the drops of metal to precipitate freely.Descending onto the hearth 21 of the vat 20, the drops fall into a metalbath communicating with the metal bath in the melting pot 10.

From the upper part of the vat 20 the slag flows by gravity over thethreshold of the discharge hole 22 into the discharge chute (not shownin the Figure) and is taken into the slag pot or directly forreprocessing. If necessary, the vat 20 is heated by burners (not shownin the Figure).

With respect to the composition the lag produced in the course of thisprocess approaches the blast furnace slag. Other compositions of theslag are also feasible which broadens the field of their utilization.

The metal 5 is discharged through channel 18 at the hearth 11 of themelting pot 10. The metal 5 can be discharged by opening the channel 18periodically, through this changes the melt level in the melting pot 10,which impairs the stability and parameters of the process. Continuousdischarge of metal 5 can be realized by maintaining the preset crosssection of the channel 18, which makes for the metal discharge at aspeed equal to the speed of its entering into the quiescent zone 8.However, such a metal discharge system is not quite reliable.

Reliable discharge of metal 5 and stable level of melt in the meltingpot 10 are ensured by the provision of metal precipitation vat 23.Flowing through the channel 18, metal 5 enters the lower part of the vat23, then rises, reaches the threshold of metal discharge hole 25 andflows by gravity into the chute (not shown in the Figure), wherefrom itis transferred into a ladle or mixer, or directly into as installationfor further conversion.

The obtained metal is used as an intermediate product for making steelin oxygen converters, electric furnaces, extra-furnace refining plants,and other installations.

The chemical processes of reduction and burning occuring in the upperbubbled zone 9 yield process gases. These gases consist, basically, ofCO and H₂ with a low content of CO₂ and H₂ O. They also contain nitrogenliberated from solid carbon fuel and from oxygen-containing gas. Processgases 6 are evolved from the melt and discharged from the upper part ofstack 12 through means 15 for the discharge of process gases.

Process gases 6 are used as fuel in furnace chambers. High qualitycharacteristics of gases (ratio of reducing components to oxidizingones) allow process gases 6 to be also utilized as a reducing agent inthe processes of solid-phase direct reduction of iron, or in blastfurnaces. The content of hydrogen in the process gases can be regulatedby changing the moisture content of the charge and by delivering steamabove the surface of the melt.

To raise the furnace output and cut down fuel consumption, also whenthere is no need nor possibility for using the reducing process gases inother installations, said gases are utilized partly or wholly directlyin the furnace. For this purpose oxygen-containing gas 3 is deliveredinto the furnace stack 12 through additional tuyeres 26. The carbonmonoxide and hydrogen evolved from the bath interact with the oxygen ofthe oxygen-containing gas 3 being oxidized to CO₂ and H₂ O. By feedingdifferent amounts of oxygen-containing gas 3 per ton of fuel it becomespossible to adjust the degree of reburning of process gases.Oxygen-containing gas 3 is fed as close as possible to the surface ofthe melt in upper bubbled zone 9 and distributed uniformly above saidsurface by adjusting the positions of the additional tuyeres 26. As aresult, a reburning flame jet is formed above the melt. The splashes ofslag and the solid particles getting into the flame jet blacken thelatter intensively and, consequently, it becomes highly radiant.

While flowing through the flame, the slag splashes are heated and returninto the bath, heating the latter. This provides for efficient transferof reburning heat to the melt. The degree of utilization of reburningheat is increased by optimizing within 1.05 to 2.0 the ratio of thehorizontal section areas of the stack in the reburning zone and in themelting pot 10 at the delivery level of oxygen-containing gas 3 into themelt and the distance from the hearth 11 to nozzles 27 of the additionaltuyeres 26 within the limits of 1.5 to 6.0 the distance from the hearth11 to the level of nozzles 14 of the tuyeres 13 and in accordance withother parameters.

After complete reburning in the furnace, discharge gases 6 containvirtually no combustible components and their utilization is confinedonly to the utilization of sensible heat.

The dust content in the discharge gases 6 is low because of the absenceof distributed loading and good assimilation of the charge by thebubbled melt.

Given below are embodiments of the hereinproposed method for preparingferrocarbon intermediate product for use in steel manufacture and afurnace for the realization thereof.

EXAMPLE 1

A melt bath in the furnace for preparing liquid ferrocarbon intermediateproduct for use in steel manufacture is formed by filling melting pot 10with liquid blast-furnace slag at 1350° C., said slag having thefollowing formula, %: SiO₂ =35.9; MnO-0.5; S=1.4; Fe_(tot) =0.5;CaO=39.9; Mg=0 to 8.7; Al₂ O₃ =9.8; other oxides, the balance.

Oxygen-containing gas 3 (O₂ =99.5%) is delivered below the melt surfacethrough tuyeres 13 with nozzles 14 at the rate of 1500 Nm³ /h per m² ofthe horizontal section area of the melt. The ratio of the horizontalsection area of melting pot 10 at the installation level of tuyeres 13to the total cross-sectional area of nozzles 14 of said tuyeres is equalto 300.

The delivery of oxygen-containing gas below the surface of the meltbrings about the formation of upper bubbled zone 9 and lower calm zone 8of the melt.

Bubbled zone 9 is loaded through charging device 16 with coal, moisturecontent 5%, in an amount ensuring a volumetric concentration of 20% inupper bubbled zone 9 of the melt; then bubbled zone 9 is loadedconcurrently with coal, through device 16, and concentrate having thefollowing composition, %: total iron, 63.5; barren rock, 10.0. Theiron-ore concentrate is loaded jointly with flux, i.e. lime, at the rateof 6 t/h. Iron-ore concentrate, flux and coal are supplied to chargingdevice 16 by a belt conveyor.

The iron-ore concentrate, together with coal and flux gets into bubbledzone 9 of the melt, is heated, melted and reduced through interactionwith coal. The heat required for keeping the melt hot. for heating,melting and reducing the raw material is produced by burning a part ofcoal due to interaction with the oxygen of oxygen-containing gas 3supplied through tuyeres 13 with nozzles 14.

Growing in size, the drops of metal precipitate from the melt of bubbledzone 9, pass through the slag layer in lower clam zone 8 and build up acalm layer of metal melt.

The process gases evolved during melting, amounting to 123000 Nm³ /h aredischarged from the furnace through a gas-discharge means 15. Thecomposition of process gases, vol.% is a follows: Co=75.0; H₂ =20.2; CO₂=2.0; N₂ =1.0.

The slag produced during melting is discharged from the furnace throughchannel 17. Composition of discharged weight %: SiO₂ =38.7; MnO=1.4;Fe_(tot) =4.0; CaO=38.4; MgO=8.9; Al₂ O₃ =10.6; Slag temperature, 1500°C.

The distance from the hearth of melting pot 10 to the upper boundary ofslag discharge channel 17 is 0.3 the distance from the lower boundary ofmetal discharge channel 18 to the installation level of tuyers 13, whithensures the discharge of slag from the level of the lower part of theslag layer in the lower calm zone 8.

The metal is discharged from the furnace through channel 18 located athearth 11 of melting pot 10. Composition of discharged weight, %: C=4.5;S=0.030; P=0.11; Si=0.15; Mn=0.16; The temperature of metal at outlet is1500° C. The furnace output is 35.4 t/h, coal consumption, 65 t/h, ironextraction, 96.85%, dust carryover, 1.2%.

EXAMPLE 2

The melting process is similar to that described in Example 1.

The ratio of the horizontal section area of melting pot 10 at theinstallation level of tuyeres 13 to the total cross-sectional area ofnozxzles 14 of said tuyeres is 10000.

Oxygen-containing gas 3 (O₂ =99.5%) is delivered at the rate of 150 Nm³/h per m² of the horizontal section area of the melt. The furnace isloaded with sponge iron at the rate of 10 t/h; the sponge iron has thefollowing composition, weight %: total iron=85, metallic iron=60, barrenrock=10.0. The consumption of flux (lime) is 0.9 t/h. Volumetricconcentration of coal in the melt of bubbled zone 9 is 0.5%. Compositionof the produced metal, weight %: C=3.8; S=0.030; P=0.11; Si=0.15;Mn=0.16. Temperature of metal at outlet=1500° C. The slag is dischargedthrough channel 17 into vat 20 where metal drops are additionallyseparated then slag is continuously discharged from vat 20 through hole22. The average horizontal section area of the slag precipitating vat 20is 0.03. the average horizontal section area of melting pot 10. Theyield of process gases is 14500 Nm³ /h. Furnace output, 8.6 t/h, coalconsumption, 8 t/h, iron extraction, 97.7%, dust carryover, 1.0%.

EXAMPLE 3

The melting process is conducted on the same lines as in Example 2. Theratio of the horizontal section area of melting pot 10 at theinstallation level of tuyeres 13 to the total area of the outletorifices of nozzles 14 of said tuyeres is 450.

The average horizontal section area of the slag precipitation vat 20 is0.3 the average horizontal section area of melting pot 10. The distancefrom the lower boundary of channel 18 of hearth 11 to the upper boundaryof channel 17 is 0.75 the distance from the lower boundary of metaldischarge channel 18 to the installation level of tuyeres 13.

The vertical distance from hearth 11 of melting pot 10 to the lower edgeof slag discharge hole 22 is 1.2 the distance from hearth 11 of meltingpot 10 to the installation level of tuyeres 13. Oxygen-containing gas 3(O₂ =50%) is delivered at the rate of 1300 Nm³ /h per m² of thehorizontal section area of the melt bath. Sponge iron is loaded at therate of 40 t/h. The volumetric concentration of coal in the melt ofbubbled zone 9 is 40%. Composition of the produced metal, weight %:coal=4.8; S=0.030; P=0.11; Si=0.15; Mn=0.16; Metal temperature atoutlet, 1500° C.

The furnace output of liquid metal os 35.2 t/h, coal consumption, 26t/h, extraction of iron into metal from iron-bearing material, 98.5%,dust carryover, 0.8%.

EXAMPLE 4

The melting process is similar to that disclosed in Example 3. Every 5 hthe delivery of coal and sponge iron is interrupted for 25 min. Theaverage sulphur content in the produced metal decreases to 0.015%.

EXAMPLE 5

The slag melt bath is built up in the furnace by pouring in liquidblast-furnace cast iron containing 4.8% C. at 1480° C. above the levelof metal discharge channel 18 but lower than the upper boundary of slagdischarge channel 17 followed by pouring in liquid blast furnace slag asin Example 1, above the level of nozzles 14 tuyenes 13. Thenoxygen-containing gas 3 (O₂ =80%) is delivered through tuyeres 13 at therate of 1000 Nm³ /h·m², thus creating bubbled zone 9 of the melt. Thenanthracite, lump size 0 to 15 mm, moisture content 5%, is delivered intobubbled zone 9 in an amount sufficient for the volumetric concentrationof said anthracite to reach 25% in the melt, after which bubbled zone 9is loaded, jointly with anthracite, with hematite ore, lump size 0 to 10mm at the rate of 80 t/h. Chemical composition of ore, weight %: totaliron 51.0; barren rock 23.5. The coke breeze is delivered in the amountof 1.4 t/h per m² of the horizontal section area of the melt. Limeconsumption, 11 t/h.

Air is delivered at the rate of 5000 Nm³ per t of coke breeze above themelt surface through additional tuyeres 26 installed in furnace stack12. The lower part 29 of furnace stack 12 has the shape of a trapezoidin a vertical cross section, the ratio of the horizontal section area ofstack 12 at the installation level of additional tuyeres 26 to thehorizontal section area of melting pot 10 at the installation level oftuyeres 13 being 2.0. Additional tuyeres 26 are installed in furnacestack 12 at the height equal to three times the distance from hearth 11to the installation level of tuyeres 13. The process gases leaving upperbubbled zone 9 of the melt are reburned with the oxygen ofoxygen-containing gas 3 fed in though additional tuyeres 26.

The heat released during this process is transferred by radiation andconvection to the melt in upper bubbled zone 9.

The gases formed after reburning are discharged from furnace stack 12through gas discharge means 15. The composition of dry gases, vol. %:CO₂. 32.0; N₂, the balance.

Slag 4 produced during melting is discharged from melting pot 10 asdescribed in Example 2. Composition of the discharged slag weight %:SiO₂ =39, MnO=1.4, Fe_(tot) =2.5, CaO=38.4, MgO=8.9, Al₂ O₃ =9.8. Slagtemperature 1550° C.

Metal 5 is discharged from melting pot 10 continuously through channel18, vat 23 and discharge hole 25.

Composition of discharged metal weight %: C=4.5; S=0.035; P=0.11;Si=0.08; Mn=0.09. Metal temperature, 1550° C. Furnace output is 40 t/h,consumption of anthracite, 28 t/h.

EXAMPLE 6

The slag melt is preliminarily built up by loading solid crushedblast-furnace slag and melting it. Then the furnace is loaded withsponge iron at the rate of 10 t/h of the following composition, mass %:total iron=98.0; metallic iron=97.0; barren rock=0.7. The delivery rateof coke breeze is 0.2 t/h per m² of the horizontal section area of themelt at the level of delivery into it of oxygen-containing gas 3. Thevolumetric content of coke breeze in bubbled zone 9 of the melt is 10%.The rate of delivery of oxygen-containing gas (O₂ =99.5%) is 200 Nm³/h·m² below the melt surface level and 10 Nm³ per t of coke breeze abovethe melt surface.

Furnace capacity, liquid product, is 9.7 t/h, comsumption of cokebreeze, 4th, iron extraction, 99.3%, dust carryover, 0.5%.

EXAMPLE 7

The process of melting is carried out along the lines specified inExample 5. Ore comsumption is 80 t/h. The solid carbon fuel isconstituted by carbonaceous waste (product of refuse pyrolysis), carboncontent 40%. The waste is loaded at the rate of 5 t/h per m² of the melthorizontal section area at the delivery level thereto ofoxygen-containing gas 3.

Furnace capacity, liquid product, 40 t/h, consumption of carbonaceouswaste, 100 t/h, extraction of iron from ore, 95%, dust carryover 0.5%.

EXAMPLE 8

The melting porcess is analogous to that described in Example 5.Oxygen-containing gas 3 is delivered concurrently with natural gas fedbelow the melt surface at the rate of 250 Nm³ /h per m² of horizontalsection area of the melt bath. The anthracite is loaded at the rate of11.15 t/h per m² while ore and lime, at 88 t/h and 1.15 t/h,respectively. Furnace capacity, liquid product, is 44.2 t/h, anthraciteconsumption, 23 t/h, degree of iron extraction into the product, 98.5%.

INDUSTRIAL APPLICABILITY

As can be concluded from the quoted data, we propose a radically newmethod of preparing liquid ferrocarbon intermediate product for use insteelmaking, said method consisting in liquid-phase reduction. Thisprocess features essential advantages over the methods known heretore.

The process does not call for the use of metallurgical coke since it issubstituted by coal or other kinds of carbon fuel or even bycarbon-containing waste,

The process does not call for the preparation of iron-ore raw materialand can be used to advantage for processing various kinds ofiron-bearing raw materials, including the kinds whose processinginvolves considerable difficulties, (e.g. slimes, dust released in gaspurification plants, steel chips).

A version of the process involving reburning permits producingferrocarbon product directly from the iron-ore raw material at a singlestage combining high output with low fuel consumption. The specificoutput per unit of useful furnace volume in the process is 2 to 3 timesthat of the best known blast furnaces.

The process ensures a high degree of iron extraction from raw materials.Losses of iron with slag do not run higher than 2 to 4% depending on theprocess parameters.

The furnace is highly reliable and simple in design, it is easy tocontrol, including the use of automation and electronic computers.Introduction of cooling elements in the zone of active slag and thepresence of a calm layer of slag above the metal bath quarantees highstability of the refractory lining and long inter-repair intervals.

The method permits producing high-quality reducing gas for technologicalpurposes.

Due to the possibility of changing their composition within broadlimits, the produced slags can be utilized to various ends, for examplefor manufacturing construction materials.

The disclosed method enables the agglomerate and coking byproductprocesses to be left out of the metallurgical cycle and reducesenvironmental pollution.

From the viewpoint of its utilization in steelmaking, the quality of theproduced ferrocarbon product is not inferior to that of blast furnacecast iron.

The disclosed method can be used as a basis for small-scale manufactureof steel (miniplants).

Economical calculations have revealed that the expenditures incurred insteelmaking according to hereinproposed method and the furnaces forrealization thereof can be 10 to 30% lower than those currently observedin the known technologies.

We claim:
 1. A method for preparng a ferrocarbon intermediate productwhich comprises:(a) forming a slag melt in a slag melt zone (b)introducing an oxygen containing gas below the surface of the slag meltat a level to form an upper bubbling slag melt zone and a lowerquiescent slag melt zone; (c) introducing a solid, carbon containingfuel and an iron containing material into the slag melt in an amountsufficient to maintain a volumetric concentration of solid carboncontaining fuel in the bubbling slag melt zone of from 0.5 to 50%,whereby additional slag and a liquid ferrocarbon intermediate productare formed, the liquid ferrocarbon intermediate product passing throughthe quiescent slag melt zone to form a layer in a ferrocarbonintermediate product zone; and (d) recovering separately the slag meltfrom the quiescent slag melt zone and the ferrocarbons intermediateproduct from the ferrocarbon intermediate product zone.
 2. A methodaccording to claim 1 wherein the slag melt zone has a horizontal sectionarea, and the oxygen-containing gas (3) is introduced into the slag meltat a rate of 150 to 1500 Nm³ /h per m² of the horizontal section area ofthe slag melt zone at the level of delivery of the oxygen-containing gas(3).
 3. A method according to claim 2, wherein the consumption ofoxygen-containing gas (3) delivered into the slag melt is increased withan increase in the reactivity of solid carbon fuel (2).
 4. A methodaccording to claim 1 wherein the oxygen-containing gas (3) iscontinuously introduced into the slag melt in the process of melting,periodically interrupting the concurrent loading of the iron-containingmaterial (1) and solid carbon fuel (2).
 5. A method according to claim 1wherein the slag melt is initially formed by pouring liquid slag intothe slag melt zone, the liquid slag produced in the manufacture offerrous metals.
 6. A method according to claim 5 wherein the pouring-inof liquid slag is preceded by pouring liquid metal into the ferrocarbonintermediate product zone.
 7. A method according to claim 1 wherein theslag melt is build up by loading and melting at least one of a solidoxide material selected from the group consisting of slag produced inthe manufaceture of ferrous metals, crude minerals, and metal oxides. 8.A method according to claim 1 wherein a gaseous, liquid or solidpulverized carbonaceous fuel is introduced into the bubbling slag meltzone.
 9. A method according to claim 1 wherein the slag (4) isdischarged from the lower quiescent slag melt zone (8) of the slag meltat the level of the middle or upper part of the zone.
 10. A methodaccording to claim 1 wherein the oxygen-containing gas (3) isadditionally delivered above the surface of the slag melt, at the rateof 0.01×10³ to 5.0 ×10³ Nm³ per ton of solid carbon fuel.
 11. A methodaccording to claim 10 wherein in the concurrent introduction of theiron-containing material (1) and solid carbon fuel (2) the solid carbonfuel is introduced at a rate of 0.2 to 5.0 t/h per m² of the horizontalsection area of the slag melt at the level delivery thereto ofoxygen-containing gas (3).
 12. A furnace for the production of aferrocarbon intermediate product comprising: a melting pot (10) havingwalls, with a hearth (11), a stack (12) having walls resting on saidmelting pot (10) and provided with at least one means (16) for chargingthe iron-containing material and solid carbon fuel into the melting pot(10), the means being arranged in the upper part of the stack (12),tuyers (13) with nozzles (14) for the delivery of oxygen-containing gasinto the melting pot (10), having a slag discharge channel (17) havingan upper boundary, arranged in the wall of the melting pot (10) abovethe hearth (11), a ferrocarbon intermediate product discharge channel(18) having a lower boundary arranged in the wall of the melting pot(10) below an installation level of tuyers (13) with nozzles (14), ameans (15) for the discharge of process gases arranged in an in upperpart of the stacl (12), wherein, the melting pot (10) and stack (12) areof an essentially rectangular shape in a horizontal section, each havinga longer wall and a shorter wall, the tuyers (13) with nozzles (14) arearranged in the longer walls of the melting pot (10), the channels (17)and (18) are arranged in the shorter walls of the melting pot (10), theratio, of the horizontal section area of the melting pot (10), at theinstallation level therein of tuyers (13) with nozzles (14), to a totalarea of the outlet holes of nozzles (14) is 300 to 10000 and thedistance (h) from the lower boundary of the slag discharge channel (17)being 0.3 to 0.75 the distance (H) from the lower boundary or productdischarge channel (18) to the installation level of tuyers (13) withnozzles (14) in the melting pot (10).
 13. A furnace according to claim12, wherein, a wall portion of the upper part of the melting pot (10)and at least a wall portion of the lower part of the stack (12) areprovided with cooling means to form a cooled portion.
 14. A furnaceaccording to claim 13, wherein, the tuyers (13) with nozzles (14) forthe delivery of oxygencontaining gas into the melting pot are installedin the cooled portion.
 15. A furnace according to claim 12 additionallycomprising a slag precipitation vat (20) with a slag discharge hole (22)for discharge of the slag melt, communicating with melting pot (10)through a slag discharge channel (17), an average area of the slagprecipitation vat (20) being 0.03 to 0.3 an average area of thehorizontal section of the melting pot (10).
 16. A furnace according toclaim 15, wherein, a vertical distance (H₁) from the hearth (11) of themelting pot (10) to a lower edge of the slag discharge hole (22) of theslag precipitation vat (20) is from 1.1 to 2.5 the distance (H₂) fromthe hearth (11) of the melting pot (10) to the installation leveltherein of tuyers (13) with nozzles (14).
 17. A furnace according toclaim 12, further comprising a ferrocarbon intermediate productintermediate product precipitation vat 23 with a ferrocarbonintermediate product discharge hole (25) arranged at a level above thehearth in communication with the melting pot (10) through a productdischarge channel (18) to provide a constant level of the product in themelting pot (10) in the course of melting during continuous discharge ofthe ferrocarbon intermediate product from the furnace.
 18. A furnaceaccording to claim 12 additionally comprises, additional tuyers (26)with nozzles (27) arranged for the delivery of oxygen-containing gasinto the stack at a level above the slag melt.
 19. A furnace accordingto claim 18 wherein the distance NH₃) from the hearth (11) of themelting pot (10) to the installation level of additional tuyers (26) ofany row is 0.5 to 6.0 the distance (H₂) from the hearth (11) of themelting pot (10) to the installation level therein of the tuyers (13).20. A furnace according to claim 18 wherein a horizontal section area ofthe stack (12) at the installation level of the additional tuyers (26)of any row is 1.05 to 2.0 the horizontal section area of the melting pot(10) at the installation level therein of the main tuyers (13).
 21. Afurnace according to claim 18 wherein, at least a lower part (29) of thestack (12) has the shape of the trapezoid in a vertical section, asmaller base of the trapezoid resting on the melting pot (10).